ABSTRACT:
In sludge
treatment, drying sludge using typical technology with high water content to a
water content of approximately 10% is always difficult because of adhesive
characteristics of sludge in drying. Many methods have been applied, including
direct and indirect heat drying, but these approaches of reducing water content
to below 40% after drying are very inefficient in energy utilization of drying
sludge. In this study, fry-drying technology with a high heat transfer
coefficient of approximately 500 W/m2·°C was used to dry swine
excreta, sewage and industrial sludge. Also waste oil was used in the
fry-drying process, and because the oil’s boiling point is between 240°C and
340°C and the specific heat is approximately 60% of that of water. In the
fry-drying system, the sludge is input by molding it into a designated form
after heating the waste oil at temperatures between 130°C and 150°C. At these
temperatures, the heated oil rapidly evaporates the water contained in the
sludge, leaving the oil itself. After approximately 8 - 10 min, the water
content of the sludge was less than 10%, and its heating value surpassed 20,000
kJ/kg. Indeed, this makes the organic sludge appropriate for use as a solid
fuel. The dried swine excreta, sewage and industrial sludge can be used in an
incinerator like low-rank coal or solid fuel.